Mind: A Brief Introduction (John R. Searle) / quote 80 of 138
Rigid designators
Kripke’s argument appeals to the concept of a “rigid designator.” A rigid designator is defined as an expression that always refers to the same object in any possible state of affairs. Thus, the expression, “Benjamin Franklin,” is a rigid designator because in the usage that I am now invoking, it always refers to the same man. This is not to say, of course, that I cannot name my dog “Benjamin Franklin,” but, then, that is a different usage, a different meaning of the expression. On the standard meaning, “Benjamin Franklin” is a rigid designator. But the expression, “The inventor of daylight saving time,” though it also refers to Benjamin Franklin, is not a rigid designator because it is easy to imagine a world in which Benjamin Franklin was not the inventor of daylight saving time. It makes sense to say that someone else, other than the actual inventor, might have been the inventor of daylight saving time, but it makes no sense to say that someone else, other than Benjamin Franklin, might have been Benjamin Franklin. For these reasons, “Benjamin Franklin” is a rigid designator, but “the inventor of daylight saving time” is nonrigid.